In recent years, there has been developed a nondestructive inspection technique using a high-frequency electromagnetic wave (hereinafter generally referred to as “terahertz wave” for convenience of description) of a range from millimeter-wave to terahertz-wave (30 GHz-30 THz). In the frequency range of the terahertz wave, there exist absorption lines of a variety of substances including biomolecules. Accordingly, as application fields of electromagnetic waves of this frequency band, there are expected a technique of performing imaging by means of a safer fluoroscopic apparatus as a substitute for X-ray, a spectral technique of determining an absorption spectrum or complex dielectric constant of the interior of a substance to examine a bonding state, a technique of analyzing biomolecules, a technique of estimating carrier concentration or mobility, and so on.
As an object inspection apparatus using a terahertz wave, there has been disclosed, as shown in FIG. 9, an apparatus for irradiating an object 4 with a terahertz wave propagating through a space and identifying the constituent material of the object 4 based on a change in the characteristics of the wave transmitted through the object 4 (Japanese Patent Application Laid-Open Nos. H08-320254 and 2002-257629). At this time, the object 4 can be two-dimensionally scanned to provide a transmission image of the interior of the object 4.
Further, although not using the frequency range of the terahertz wave, there has been disclosed a technique relating to an inspection apparatus obtained by integrating such an inspection apparatus (Japanese Patent Application Laid-Open No. H06-018421). As shown in FIG. 10, in this device 11, semiconductors 1, 6 having light emitting elements 2 and light receiving elements 7, respectively, are joined and integrated with a gap corresponding to a flow path 10 being present therebetween. The device 11 measures the concentration of an objective component existing in the flow path 10 based on a change in a light propagating from the light emitting elements 2.
Moreover, as a constitutional example of an optically gated terahertz transmitter/receiver for transmitting/receiving a terahertz wave, an antenna structure formed on a semiconductor substrate, as shown in FIGS. 11A and 11B, is used in many cases. When transmitting a terahertz wave, as shown in FIG. 11A, a gap between dipole antennas of a PC antenna is irradiated with a laser light under application of a DC bias voltage between transmission lines. On the other hand, when receiving a terahertz wave, as shown in FIG. 11B, in a state in which a gap between dipole antennas of a PC antenna is irradiated with a laser light, an electric current flow between transmission lines generated by incidence of a terahertz wave on a substrate is measured by an ammeter.
Water has a strong absorption spectrum for the terahertz wave. Accordingly, as with Japanese Patent Application Laid-Open No. H08-320254 above, when a terahertz wave is allowed to propagate through the atmosphere, the electromagnetic wave will be remarkably attenuated by the influence of water existing in the atmosphere. To reduce the influence of the atmosphere on an electromagnetic wave, there is needed, for example, a means of adjusting the environment at least with respect to a region surrounding the propagation path of the electromagnetic wave. In this case, there is a problem that the provision of the means of adjusting the environment makes the apparatus large-sized. Also, there is another problem that the characteristics of substances present in the atmosphere are liable to be simultaneously detected to thereby sense unwanted signal components, thus increasing noise components.